Hi, I was trying to use the skin for composite object following the documentation example: <bodypos="0 0 1"> <freejoint/> <composite type="box" count="7 7 7" spacing="0.04"> <skin texcoord="true" material="matsponge" rgba=".7 .7 .7 1"/> <geomtype="capsule" size=".015 0.05" rgba=".8 .2 .1 1" /> </composite> </body> However I got the following error: MuJoCo Pro version 2.00 Error: material 'matsponge' not found in skin 0 Object name = CSkin, id = 0 Anyone can help? Thanks!